1. Field of the Invention
The present invention relates to a flat panel image display apparatus adapted for use as a character or image display apparatus such as a display or a message board of a television receiver, a computer or the like.
2. Related Background Art
There is being commercialized a flat panel image display apparatus utilizing cold cathode electron-emitting devices such as a field emission type or a surface conduction type. The detailed configuration of such flat panel image display apparatus is disclosed in the Japanese Patent Application Laid-Open No. 07-235255.
As the above-described electron-emitting device requires high vacuum at least equal to 10xe2x88x926 Torr for operation, there is required a vacuum envelope for constituting the image display apparatus employing such cold cathode electron-emitting device. Since the vacuum envelope is subjected to an external force caused by the pressure difference between the external atmospheric pressure and the pressure inside the vacuum envelope, there is required a support structure for maintaining the distance inside the vacuum envelope. In the absence of such support structure, the external force is supported by increasing the thickness of the constituents, but such configuration results in a drawback of an increased weight.
In consideration of the foregoing, there is proposed an image forming apparatus employing a vacuum envelope utilizing a spacer (Japanese Patent Application Laid-Open No. 07-302560). FIG. 8 illustrates a vacuum envelope of an image display apparatus utilizing the cold cathode electron-emitting device, wherein shown is a rear plate 1; a face plate 2 having a phosphor (not shown) and opposed to the rear plate 1; an outer frame 3 for connecting the periphery of the rear plate 1 and the face plate 2; flat plate-shaped spacers 4; and plural electron-emitting devices 5 mounted on the rear plate 1.
A support structure utilizing plural spacers is enabled to withstand the atmospheric pressure applied to the vacuum envelope. As a result, the rear plate 1 and the face plate 2 constituting the vacuum envelope can be made thinner to realize a vacuum envelope of a lighter weight and a larger area, whereby an image display apparatus of flat panel type can be realized.
Conventionally, the image quality may be deteriorated by the deformation of the vacuum envelope. The object of the present invention is to realize a more desirable configuration of the support structure for the vacuum envelope.
The above-mentioned object can be attained, according to the present invention, by a vacuum envelope constituted at least by a first substrate, a second substrate opposed to the first substrate with a predetermined distance thereto and plural spacers positioned between the first and second substrates, wherein a ratio xcex7 of the vacuum envelop is defined by S/A in which A is the internal cross sectional area of the vacuum envelope in a cross section parallel to the principal plane of the first or second substrate and S is the total cross sectional area of the plural spacers on such cross section and satisfies a relation 0.018%xe2x89xa6xcex7xe2x89xa67.8%.
According to the present invention there is also provided an image display apparatus utilizing the vacuum envelope.